Safety mechanism for a hydraulically operated dockboard

ABSTRACT

A safety mechanism to be incorporated with a hydraulically operated dockboard for preventing free descent of the ramp if a carrier pulls away from the dock when a load is on the ramp. The dockboard includes a ramp having its rear edge hinged to the dock and adapted to be raised upwardly to an inclined position by a hydraulic cylinder unit. The safety mechanism is located in the hydraulic supply line that supplies hydraulic fluid to the cylinder unit from a pump and the mechanism includes a pair of valves, one of which is biased to a normally closed position and the second valve is biased to a partially open position. To raise the ramp, the pump is operated and the pressurized fluid acts to move both valves to the fully open position. When the ramp is lowered in normal operation, the hydraulic fluid being displaced from the cylinder unit passes through the partially open second valve to provide a slow rate of descent from the ramp. If a truck or carrier pulls away from the dock when a load is on the ramp, the combined weight of the ramp and the load will increase the force of the hydraulic fluid flowing from the cylinder to the pump, thereby overcoming the spring force on the second valve and moving the second valve to a fully closed position. The closing of the second valve will prevent descent of the ramp and will retain the ramp in that position until the load is removed from the ramp.

United States Patent Bregantini [151 3,656,199 [451 Apr. 18, 1972 [54]SAFETY MECHANISM FOR A HYDRAULICALLY OPERATED DOCKBOARD [72] Inventor:Robert R. Bregantini, Menomonee Falls,

Wis.

[73] Assignee: Kelley Company, Inc., Milwaukee, Wis.

[22] Filed: Nov. 2, 1970 [21] Appl. No.: 85,901

Primary Examiner-Jacob L. Nackenoff At!0rney-Andrus, Sceales, Starke &Sawall [57] ABSTRACT A safety mechanism to be incorporated with ahydraulically operated dockboard for preventing free descent of the rampif a carrier pulls away from the dock when a load is on the ramp. Thedockboard includes a ramp having its rear edge hinged to the dock andadapted to be raised upwardly to an inclined position by a hydrauliccylinder unit. The safety mechanism is located in the hydraulic supplyline that supplies hydraulic fluid to the cylinder unit from a pump andthe mechanism includes a pair of valves, one of which is biased to anormally closed position and the second valve is biased to a partiallyopen position. To raise the ramp, the pump is operated and thepressurized fluid acts to move both valves to the fully open position.When the ramp is lowered in normal operation, the hydraulic fluid beingdisplaced from the cylinder unit passes through the partially opensecond valve to provide a slow rate of descent from the ramp. If a truckor carrier pulls away from the dock when a load is on the ramp, thecombined weight of the ramp and the load will increase the force of thehydraulic fluid flowing from the cylinder to the pump, therebyovercoming the spring force on the second valve and moving the secondvalve to a fully closed position. The closing of the second valve willprevent descent of the ramp and will retain the ramp in that positionuntil the load is removed from the ramp.

9 Claims, 6 Drawing Figures PATENTEUAPR 18 m2 SHEET 1 BF 2 INVENTOR.Robert R. Bregcmtmi Attorneys SAFETY MECHANISM FOR A HYDRAULICALLYOPERATED DOCKBOARD This invention relates to a dockboard and moreparticularly to a safety device for a hydraulically operated dockboardwhich prevents free descent of the ramp in the event a carrier pullsaway from the dock when a load is on the ramp.

The conventional hydraulically operated dockboard is installed in ashallow depression or pit formed in the upper surface of the clock. Thedockboard includes a ramp which is hinged at its rear edge to the backof the dock pit and when not in use the ramp is in a cross-trafficposition, generally flush with the upper surface of the dock. With thistype of dockboard, the ramp is adapted to be pivoted upwardly to aninclined position by a hydraulic cylinder unit which is connectedbetween the ramp and the supporting structure. When a truck or othercarrier backs toward the dock, the cylinder unit is extended to move theramp upwardly to the inclined position, and simultaneously, an extensionlip which is hinged to the front edge of the ramp and is moved by secondhydraulic cylinder unit from a pendant position to a partially extendedposition. Upward movement of the ramp also actuates a lip latchingmechanism which engages the lip and holds it in the partially extendedposition. With the ramp in the upwardly inclined position and the lipextended, the operator then shuts off the pump motor and the ramp willslowly lower by gravity, displacing the hydraulic fluid from thecylinder, until the lip moves into engagement with the bed of thecarrier. As the lip engages the carrier, it is moved to its fullyextended position thereby releasing the lip latching mechanism.

When the loading is completed and the truck pulls away from the dock,the ramp will continue to lower, if above dock level, until projectionsor legs at the front of the ramp engage stops on the frame or supportingstructure. If the ramp is at a below dock level position during theloading operation, the ramp will continue to move downwardly by gravity,when the truck pulls away from the dock, to its lowermost below docklevel position, until the ramp hits stops on the dock and this willactuate a switch to start the pump and automatically raise the ramp tothe cross traffic position.

In the past, problems have arisen when the carrier would pull away fromthe dock, when a lift truck or other heavy load was on the ramp. Thisadditional load on the ramp, which may be thousands of pounds, wouldcause the ramp to move downwardly at a substantially increased rate ofspeed with the result that personnel or equipment on the ramp, orportions of the hydraulic system were apt to be injured or damaged whenthe ramp descent was stopped.

The present invention is directed to a safety device for a hydraulicallyactuated dockboard which will prevent the descent of the ramp insituations where a carrier pulls away from the dock when a load is onthe ramp. The safety mechanism includes a valve assembly which isconnected to the conduit leading from the discharge side of the pump tothe hydraulic cylinder which operates the ramp. The valve assemblyincludes a pair of valves one of which is spring biased to a normallyclosed position, and the second of the valves is biased to an openposition. To raise the ramp to the inclined position the pump isoperated and the pressurized fluid acts to move both of the valves to afully open position to thereby supply fluid from the pump to thehydraulic cylinder.

When it is desired to lower the ramp under normal operatin g conditions,the pump is stopped and the ramp will descend by gravity, forcing thefluid from the cylinder back to the pump. As the first valve is biasedto a closed position, the fluid returning to the pump will pass throughthe partially open second valve to provide a slow rate of descent forthe ramp. The biasing force on the second valve is greater than theforce exerted by the fluid being displaced from the cylinder so that thesecond valve will remain partially open as the ramp descends.

In the event that a carrier pulls away from the loading clock when aleavy load, such as a fork lift truck, is on the ramp, the combinedweight of the ramp and the load will increase the pressure of thehydraulic fluid and this increased force of the fluid will overcome thespring bias on the second valve to move the second valve to the fullyclosed position. With both valves in the fully closed position, thedescent of the ramp will be stopped and the ramp will be retained inthat position until the added load is removed from the ramp. Thus, thepresent invention provides a safety mechanism which will prevent freedescent of the ramp in situations where a predetermined added load is onthe ramp, but will permit free controlled descent of the ramp wherethere is no added load on the ramp.

Other objects and advantages will appear in the course of the followingdescriptions.

The drawings illustrate the best mode presently contemplated of carryingout the invention.

In the drawings:

FIG. 1 is a perspective view of a hydraulically operated dockboardincorporating the safety mechanism of the invention, with the ramp shownin the upwardly inclined position;

FIG. 2 is a schematic view of the hydraulic system for operating theramp;

FIG. 3 is a section of the valve assembly showing one valve in theclosed position and the second valve in the partially open position;

FIG. 4 is a view similar to FIG. 3, showing both valves in the fullyopened position;

FIG. 5 is a view similar to FIG. 3, showing both valves in the closedposition; and

FIG. 6 is an end view of the valve assembly.

The drawings illustrate a loading dock 1 formed with a shallow pit ordepression 2 and a dockboard 3 is installed in the pit. The dockboard 3is provided with a structural mounting frame 4, which is mounted in thepit and the rear edge of a ramp 5 is hinged to the frame 4 at the rearof the pit. Ramp 4 includes a generally flat tread plate 6, which issupported by a series of channel-shaped parallel beams 7, and theforward edges of the beam 7 are welded together by a front plate 8.

An extension lip 9 is pivotally connected or hinged to the forward edgeof the ramp 5. To provide the hinged connection, a series of hingedsockets 10 are welded to the under surface of the lip and a secondseries of hinge sockets are welded to the front plate of the ramp. Hingepins 11 extend through the aligned sockets to provide the hingeconnection between the lip 9 and the ramp 5.

In the cross-traffic position the ramp 5 will be substantially flushwith the upper surface of the dock and the lip 9 will as sume a pendantposition in which it hangs downwardly in front of the ramp. As the rampis pivoted upwardly to an inclined position, as illustrated in FIG. 1,the lip 9 will also be pivoted outwardly to a partially extendedposition by a hydraulic cylinder unit, not shown.

The ramp is moved to the upwardly inclined position by a hydraulic unitwhich includes a cylinder 12 and a ram or piston rod 13. As shown inFIG. 1, the upper end of the cylinder 12 is pivotally connected to theundersurface of the ramp and the outer end of the ram 13 is pivotallyconnected to lugs 14, secured to the frame 4 of the dockboard. Bysupplying hydraulic fluid to the cylinder 12, the ram 13 will move tothe extended position, to thereby pivot the ramp 5 fo the inclinedposition as illustrated in FIG. 1.

The hydraulic system for supplying hydraulic fluid to the cylinder isillustrated schematically in FIG. 2.. As shown in FIG. 2, a line 15connects a fluid reservoir 16 with the inlet side of a pump 17 driven bymotor 18, and a line 19 connects the discharge side of the pump to theinlet of a valve assembly 20. Line 21 connects the outlet of the valveassembly to the cylinder 12.

The safety device of the invention is incorporated in the valve assembly20, which is best illustrated in FIGS. 3-6. The valve assembly 20includes a casing or valve block 22 having a passage 23, and the line19, which is connected to the discharge side of the pump, is threaded.into the passage 23, so that hydraulic fluid will be supplied from thepump to the passage 23. The inner end of passage .23 communicates withan enlarged passage 24 that defines a valve seat 25. A ball valve 26 isadapted to engage the valve seat 25, and valve 26 is biased to thenormally closed position by a coil spring 27. One end of the spring 27bears against the valve 26, while the opposite end of the spring isretained within a recess 28 formed in the inner end of the stud 29 isthreaded within the outer end of the passage 24. A sealing gasket 30 islocated between the head of the stud 29 and the outer wall of the valveblock 22.

As shown in FIGS. 3-5, a cross passage 31 is connected between thecentral portion of passage 23 and a passage 32 which is substantiallyparallel to the passage 23. The end of passage 32 communicates with anenlarged passage 33 which defines a valve seat 34. A ball valve 35 isadapted to seat on the valve seat 34.

The ball valve 35 is biased to a partially open position by a pair ofcoil springs 36 and 37 which act against opposite portions of the ballvalve. One end of the spring 36 bears against the ball valve 35, whilethe opposite end of the spring is retained around a projection 38 formedon the inner end of stud 39, which is threaded within the outer end ofthe passage 33. A sealing gasket 40 is located between the head of thestud and the wall of the valve block 22.

Spring 37 acts on the opposite side of the ball valve 35, and the outerend of the spring 37 is retained within a recess 41 formed in the innerend of a stud 42 that is threaded within the enlarged passage 43 thatcommunicates with passage 32.

A sealing gasket is located between the outer wall of the valve block 22and a jam nut 44 threaded on the stud 42. A lock nut 45 is threaded onthe outer end of stud 42 and the projecting end of stud 42 is providedwith a slot to receive a screw driver, or other tool to provide anadjustment of the spring force on the valve 35. By loosening the nuts 44and 45 and adjusting the position of the stud 42, the force of thespring 37 can be varied to thereby adjust the relative location of theball valve 35 with relation to the valve seat 34. Valve 35 is acted onby both springs 36 and 37 and due to the fact that the force of spring37 is greater than the force of the spring 36 the valve will be normallybiased to the partially open position. By adjustment of the stud 42, theforce of the spring 37 can be varied to thereby regulate the forcenecessary to move the valve 35 to the fully closed position.

A cross passage 46 connects the passages 33 and 24, and an outletpassage 47 is connected to the passage 33 and extends to the exterior ofthe valve block. The fluid line 21, which extends to the cylinder 12, isthreaded into the outlet passage 47.

Under normal no-load conditions, the valves 26 and 35 will be in theposition shown in FIG. 3, in which the valve 26 is closed and the valve35 is biased by springs 36 and 37 to a partially open position. When itis desired to elevate the ramp, the pump is operated and the pressurizedfluid acting within the passage 23 will move the valve 26 to the fullyopened position, as shown in FIG. 4. The pressurized fluid will also actthrough the passages 31 and 32 to move the valve 35 to the fully openposition so that the fluid will pass through both open valves throughthe outlet passage 47 to the cylinder. When the ramp has been elevatedto the inclined position and the lip 9 has been moved outwardly to thepartially extended position, the operation of the pump is terminated andthe ramp will then descend by gravity until the lip 9 engages the bed ofthe truck or other carrier. As the ramp descends the weight of the rampwill act to move the cylinder and piston to a retracted position causingthe hydraulic fluid to be displaced from the cylinder and pass into thevalve block 22 through the passage 47. In this situation, the force ofthe hydraulic fluid in the passage 47, plus the force of the spring 36is slightly less than the force of the spring 37 so that the valve 35will be in a partially open position to provide a restricted flow of thehydraulic fluid through the passages 32, 31 and 23 to the pump. The pumpis designed so that the fluid will flow through the pump to thereservoir during non-operating conditions. Thus, the fluid will flow ina restricted manner through the partially open valve 35 to the pump, toprovide a slow rate of descent for the ramp from its upwardly inclinedposition until the lip engages the bed of the carrier.

After the loading operation has been completed and the carrier pullsaway from the dock, the ramp, if it is above dock level, will lower bygravity to the cross-traffic position, at which position the crosstraffic legs 48 on the ramp engage the stops 49, and during the loweringthe hydraulic fluid being displaced from the cylinder will flow throughthe partially open valve 35 to the pump and reservoir. The legs 48 canbe of a construction similar to that shown in US. Pat. No. 3,137,017.

If the ramp, when the carrier pulls away, is in a below dock levelposition, in which case the legs 48 are retracted, the ramp willsimilarly descend slowly as the fluid flows through the partially openedvalve 35 until the ramp frame engages the stops 49 and this will actuatea switch to start the pump and return the ramp to the cross trafficposition. Thus, when the ramp descends by gravity with no added weightthereon, the hydraulic fluid will flow at a restricted rate through thepartially open valve 35 to provide a slow rate of descent for the ramp.In this situation, the valves are in the position of FIG. 3.

In the event that the truck or other carrier pulls away from the dockwhen there is an additional load on the ramp, as for example, a lifttruck or other cargo which may weigh several thousand pounds, theadditional weight on the ramp will increase the pressure of thehydraulic fluid being displaced from the cylinder so that the forceexerted by the fluid in combination with the force of spring 36 willovercome the force of spring 37, thereby moving the valve 35 to thefully closed position. As the valve 26 is also in the fully closedposition, there will be no flow of fluid through the valve assembly withthe result that the ramp bearing the additional load will be lockedagainst downward movement and will be retained in this locked positionuntil the added load is removed from the ramp. With the load removedfrom the ramp, the force of the spring 37 will again overcome thecombined force exerted by spring 36 and the hydraulic fluid so that thevalve 35 will be returned to the partially open position to permit freedescent of the ramp.

The valve 26 is not essential to the operation of the mechanism, but isdesirable in that it provides an increased rate of flow to the cylinderfor elevation of the ramp. As the passage 32 is partially restricted bythe spring 37, the valve 26 provides a secondary route for fluid flow tothe cylinder to thereby provide a more rapid rate of ramp elevation.

The valve mechanism of the invention provides a full flow of hydraulicfluid from the pump to the cylinder in order to raise the ramp. Undernormal conditions, the valve mechanism provides a restricted return offluid from the cylinder to provide a slow and controlled rate of descentfor the ramp. Under conditions where an added predetermined load is onthe ramp when the carrier pulls away from the dock, the mechanism willprevent descent of the ramp until the load is removed. This latterfeature will prevent rapid downward movement of the ramp due to theadditional weight of the load and thus serves to protect personnel,loading equipment and material being handled, as well as protecting thedockboard against structural or other damage.

By the simple adjustment of stud 42, the biasing force on valve 35 canbe changed to thereby vary the amount of additional load on the rampwhich is necessary to move the valve 35 to the fully closed position andlock the ramp against descent.

While the above invention has illustrated the safety mechanism inconjunction with a pit mounted dockboard, it is contemplated that thesafety mechanism can be incorporated with any hydraulically operateddockboard.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

Iclaim:

1. In a dockboard, a supporting structure, a ramp mounted for movementon the supporting structure between a storage position and an upperposition, hydraulic means for moving the ramp between the storageposition and the upper position, said hydraulic means including ahydraulic power unit interconnecting the ramp and the supportingstructure and said hydraulic means including a pump and conduit meansconnecting the discharge side of the pump and said power unit, valvemeans located in said conduit means, and biasing means for biasing saidvalve means toward an open position, said biasing means being arrangedso that fluid being discharged from the pump to the power unit to raisethe ramp will act in conjunction with said biasing means to move thevalve means to a fully open position, said biasing means being arrangedso that the force of the fluid being displaced from the power unit asthe ramp is lowered under normal conditions will not overcome the forceof said biasing means so that said valve means will be in a partiallyopen position, and said biasing means being arranged so that the forceof the fluid being displaced from the power unit when the ramp descendswith an additional predetermined load applied thereto will overcome theforce of said biasing means so that the valve means will be moved to aclosed position and prevent further descent of the ramp.

2. The dockboard of claim 1, wherein said biasing means comprises a pairof resilient members with a first of said resilient members urging saidvalve means toward an open position and a second of said resilientmembers urging said valve means toward a closed position, the force ofsaid first resilient member being greater than the force of said secondresilient member whereby said valve means is biased to a partially openposition under no-load fluid pressure conditions.

3. The dockboard of claim 2, wherein said valve means comprises a valveseat and a generally spherical ball valve, said resilient members beingcoil springs disposed in engagement with opposite portions of said ballvalve.

4. The dockboard of claim 1, and including means for ad justing theforce of said biasing means to thereby regulate the amount of saidadditional load necessary to move said valve means to the closedposition.

5. The dockboard of claim 1, wherein said valve means comprises a casinghaving a passage comprising a part of said conduit means and defining avalve seat, said valve means also including a valve member adapted toengage the valve seat, said biasing means comprises a pair of resilientmembers with a first of said resilient members urging said valve membertoward an open position and a second of said resilient members urgingsaid valve member toward a closed position, the force of said firstresilient member being greater than the force of said second resilientmember whereby said valve member is biased to a partially open positionunder no-load fluid pressure conditions, and adjusting means foradjusting the force of at least one of said resilient members to therebyregulate the amount of said additional load necessary to move said valvemember to the closed position.

6. The dockboard of claim 5, wherein said adjusting means is located onthe exterior of said casing.

7. The dockboard of claim 1, and including check valve means disposed insaid conduit means in parallel arrangement with said first valve meansfor permitting flow of fluid in a direction from the pump to the powerunit and for preventing flow in the opposite direction.

8. The dockboard of claim 5, wherein said casing defines a secondpassage disposed in parallel arrangement with said first passage andconstituting a part of said conduit means, said second passage defininga second valve seat, said dockboard also including a second valveadapted to engage said second valve seat, and second biasing means forurging said second valve member to the closed position.

9. The dockboard of claim )1, wherein said power unit is a hydrauliccylinder.

1. In a dockboard, a supporting structure, a ramp mounted for movementon the supporting structure between a storage position and an upperposition, hydraulic means for moving the ramp between the storageposition and the upper position, said hydraulic means including ahydraulic power unit interconnecting the ramp and the supportingstructure and said hydraulic means including a pump and conduit meansconnecting the discharge side of the pump and said power unit, valvemeans located in said conduit means, and biasing means for biasing saidvalve means toward an open position, said biasing means being arrangedso that fluid being discharged from the pump to the power unit to raisethe ramp will act in conjunction with said biasing means to move thevalve means to a fully open position, said biasing means being arrangedso that the force of the fluid being displaced from the power unit asthe ramp is lowered under normal conditions will not overcome the forceof said biasing means so that said valve means will be in a partiallyopen position, and said biasing means being arranged so that the forceof the fluid being displaced from the power unit when the ramp descendswith an additional predetermined load applied thereto will overcome theforce of said biasing means so that the valve means will be moved to aclosed position and prevent further descent of the ramp.
 2. Thedockboard of claim 1, wherein said biasing means comprises a pair ofresilient members with a first of said resilient members urging saidvalve means toward an open position and a second of said resilientmembers urging said valve means toward a closed position, the force ofsaid first resilient member being greater than the force of said secondresilient member whereby said valve means is biased to a partially openposition under no-load fluid pressure conditions.
 3. The dockboard ofclaim 2, wherein said valve means comprises a valve seat and a generallyspherical ball valve, said resilient members being coil springs disposedin engagement with opposite portions of said ball valve.
 4. Thedockboard of claim 1, and including means for adjusting the force ofsaid biasing means to thereby regulate the amount of said additionalload necessary to move said valve means to the closed position.
 5. Thedockboard of claim 1, wherein said valve means comprises a casing havinga passage comprising a part of said conduit means and defining a valveseat, said valve means also including a valve member adapted to engagethe valve seat, said biasing means comprises a pair of resilient memberswith a first of said resilient members urging said valve member towardan open position and a second of said resilient members urging saidvalve member toward a closed position, the force of said first resilientmember being greater than the force of said second resilient memberwhereby said valve member is biased to a partially open position underno-load fluid pressure conditions, and adjusting means for adjusting theforce of at least one of said resilient members to thereby regulate theamount of said additional load necessary to move said valve member tothe closed position.
 6. The dockboard of claim 5, wherein said adjustingmeans is located on the exterior of said casing.
 7. The dockboard ofclaim 1, and including check valve means disposed in said conduit meansin parallel arrangement with said first valve means for permitting flowof fluid in a direction from the pump to the power unit and forpreventing flow in the opposite direction.
 8. The dockboard of claim 5,wherein said casing defines a second passage disposed in parallelarrangement with said first passage and constituting a part of saidconduit means, said second passage defining a second valve seat, saiddockboard also including a second valve adapted to engage said secondvalve seat, and second biasing means for urging said second valve memberto the closed position.
 9. The dockboard of claim 1, wherein said powerunit is a hydraulic cylinder.